RF DAC with configurable DAC mixer interface and configurable mixer

ABSTRACT

One embodiment of the present disclosure relates to a circuit. The circuit includes a digital to analog converter (DAC) configured to convert a time-varying, multi-bit digital value to a corresponding time-varying output current. The circuit also includes a mixer module downstream of the DAC and comprising a plurality of mixers. A control block is configured to selectively steer output current from the DAC to different mixers of the mixer module. Other techniques are also described.

REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.13/106,963 filed on May 13, 2011.

BACKGROUND

Wireless communication may be used to transfer information over manydistances, ranging from short distances (a few meters as in televisionremote control) to long distances (thousands or millions of kilometersfor radio communications). Wireless communication encompasses varioustypes of fixed, mobile, and portable two-way radios, cellulartelephones, personal digital assistants (PDAs), and wireless networking.Typical wireless devices communicate according to predeterminedcommunication protocols, such as IEEE communication standards or othertelecommunications standards, for example. Although there are manydifferent communication standards, any given standard specifies preciserules for communication, thereby helping to ensure that wireless devicesfrom different manufacturers communicate effectively with one another.

Modern wireless communication devices are integrating more and morecommunication functions into a single device. For example, a singleconventional mobile phone can transmit and receive data using multiplecommunication standards, such as 2G and 3G telecommunication standards.These standards can require different transmission powers, differentmodulation techniques, different transmission frequencies, and the like.

In order to allow a single wireless device to transmit according todifferent communication standards, conventional wireless communicationdevices include multiple transmission paths and/or reception paths. Forexample, FIG. 1 shows a portion of a conventional wireless transceiver100 that includes a first transmission path 102 on which a 3G signal istransmitted and a second transmission path 104 on which a 2G signal istransmitted. Both transmission paths 102, 104 include digital to analogconverters (DACs) 106 and mixers 108, wherein low-pass filters 110 aredisposed between the DACs 106 and their corresponding mixers 108.

For a reasonable current consumption, a 3G vector modulator is weak innoise performance, so inter-stage surface acoustical wave (SAW) filters112 are required for each transmission band, as shown in FIG. 2. TheseSAW filters 112 are coupled between the output of transmission path 102(which supports multiple transmission bands, e.g., TX_(—)3G_H,TX_(—)3G_L, TX_(—)3G_M1), and corresponding power amplifiers (PA) 114used for transmission over the corresponding bands. The need for thedifferent SAW filters 112 increases the pin count of the transceiver100, as well as the size of the printed circuit board (PCB), and theoverall bill of materials (BOM).

In view of these conventional communication devices, the inventors haveappreciated that it would be helpful from a cost and power perspectiveto provide a single, flexible transmission path that is shared formultiple communication standards rather than using separate transmissionpaths for each communication standard. Also, it would be beneficial toeliminate the need for SAW filters to reduce the pin count of thetransceiver, the size of the printed circuit board (PCB), and theoverall bill of materials (BOM) used for the transceiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a conventional transceiver thatincludes multiple transmission paths and filters thereon.

FIG. 2 is a schematic of transceiver including a transmission path.

FIG. 3 is a block diagram of a transmitter in accordance with someembodiments.

FIG. 4 is a schematic diagram of a circuit that can be included in atransmitter in accordance with some embodiments.

FIG. 5 is a chart illustrating some examples of digital values andcontrol values that can be used to achieve various transmissionconditions consistent with FIG. 4's embodiment.

FIG. 6 is a block diagram of a mixer in accordance with someembodiments.

FIGS. 7A-7B are a block diagram of a circuit that can be included in atransmitter in accordance with some embodiments.

FIG. 8 is a flow chart illustrating a method in accordance with someembodiments.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings. In the following description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the claimed subject matter. It may be evident, however,that the claimed subject matter may be practiced without these specificdetails.

Techniques disclosed herein generate a time-varying current using adigital to analog converter (DAC), and selectively steer current fromthe DAC to different mixers of a mixer module. In many embodiments, thisconfiguration limits the need for filters on the transmission path,thereby limiting the overall circuitry needed for the transceiver,relative to conventional solutions.

FIG. 3 shows an example of a circuit 300 in accordance with someembodiments. As will be appreciated in more detail below, the circuit300 provides a single transmission path that can be used for one or morecommunication protocols, wherein the circuit 300 can potentiallytransmit using a different transmission power to carry out differentcommunication protocols (and/or can use different transmission powerswithin a given communication protocol). For example, in someimplementations, the circuit can transmit according to at least two of:Global System for Mobile Communication (GSM), Gaussian minimum shiftkeying (GMSK), Enhanced Data Rates for GSM Evolution) EDGE, UniversalMobile Telecommunication Systems (UMTS), Long Term Evolution (LTE),WiMax, Bluetooth, a wireless 801.11 protocol, and/or other communicationprotocols.

The circuit 300 includes a digital to analog converter (DAC) 302, aswitch matrix 304, a mixer module 306, and a control block 308; whichare operably coupled as shown. The mixer module 306 includes a pluralityof mixers, which are operable to deliver an RF output signal to an RFantenna 310 through a power amplifier 312. In some embodiments, nofilters are required between the DAC 302 and the mixer module 306, andSAW filters are not required between the mixer module 306 and the poweramplifier 312. Hence, the circuit 300 tends to reduce area and powerconsumption, relative to conventional solutions. It will be appreciatedthat not all of these components are required in all implementations—forexample the power amplifier 312 can be omitted in some embodiments.

During operation, the output power range of the antenna 310 is dividedinto M sub-ranges (M can be an integer ranging from 2 to nearlyinfinity). At any given time, an N-bit digital value (N can be aninteger ranging from 1 to nearly infinity), which is indicative of theoutput power to be used at that time, is received on an input (314) ofthe DAC 302. The DAC 302 converts the N-bit digital value to acorresponding time-varying output current provided at an output (316) ofthe DAC 302. Thus, by changing the N-bit digital value on 314 over time,the output current on 316 can be changed over time to correspond to adesired transmission power.

The switch matrix 304, under the direction of the control block 308, isconfigured to steer various amounts of output current from the DAC 302to different mixers of the mixer module 306 based on a control signal on318 from the control block 308. The mixer module 306 then modulates thesignal from switch matrix output 320 with an LO signal 322 to deliver anRF signal 324 at a desired power level to the power amplifier 312. Thepower amplifier 312 then amplifies the RF signal 324, therebyfacilitating transmission over the RF antenna 310 at the desiredtransmission power.

The output of the control block 308 can depend on different transmissionconditions such as DAC instantaneous value, DAC biasing condition,output power, transmission standard, and crest factor, among others. Forexample, if a relatively high power signal is to be transmitted from theRF antenna 310 during a first time (e.g., while a first communicationprotocol is employed), the switch matrix 304 steers a relatively largecurrent to the mixer module 306, such that the RF antenna 310 transmitsa relatively intense RF signal. In contrast, if a relatively low powersignal is to be transmitted from the RF antenna during a second time(e.g., while a second communication protocol is employed), the switchmatrix 304 steers a relatively small current to the mixer module 306,such that the RF antenna 310 transmits a relatively low-intensity RFsignal. Typically, the DAC 302 and switch matrix 304 work in coordinatedfashion to deliver a large number of output transmission powers via theantenna 310, thereby helping a single transmission path flexibly tocarry out multiple communication protocols having different transmissionpowers.

It will be appreciated that the control block 308 can take various formsdepending on the implementation. In some embodiments, the control blockcan include a microprocessor that executes a series of instructions(e.g., software and/or firmware) as accessed from a memory unit. Inother embodiments the control block can be an application specificintegrated circuit (ASIC) or some other logic unit (e.g., FPGA, basebandprocessor).

FIG. 4 shows another circuit 400 in accordance with some embodiments.Like FIG. 3's implementation, FIG. 4's circuit 400 includes a digital toanalog converter (DAC) 402, a switch matrix 404, a mixer module 406, anda control block 408; which are operably coupled as shown.

The DAC 402 receives a time-varying N-bit digital value and converts itto a time-varying output current. To facilitate this functionality, theDAC comprises a number of current sources 410 arranged in a number ofrows and columns (where individual current sources are labeled asS_(row-column)). The current sources 410 can be selectively andindependently activated by a row decoder 412 and column decoder 414,which collectively enable logical gates (e.g., AND gate 416) havingtheir outputs coupled to respective control terminals of the currentsources 410. The current sources along a column are arranged so theiroutput currents add together if they are concurrently enabled. It willbe appreciated that, although only three columns are illustrated forsake of simplicity, other non-illustrated embodiments can include anynumber of columns. Also, although logical AND gates are illustrated, anynumber of other logical gates could also be used.

The switch matrix 404 comprises a number of switching elements coupledbetween the DAC 402 and the mixer module 406. The switching elements arearranged to selectively steer different amounts of current from the DAC402 to the mixers of the mixer module 406. For example, a first subgroupof switching elements 418 have respective first contacts coupled to afirst column of the DAC 402 and have respective second contacts coupledto different mixers in the plurality of mixers 406. A second subgroup ofswitching elements 420 have respective first contacts coupled to asecond column of the DAC and have respective second contacts coupled todifferent mixers in the plurality of mixers. A third subgroup ofswitching elements 422 have respective first contacts coupled to a thirdcolumn of the DAC 402 and have respective second contacts coupled todifferent mixers in the plurality of mixers. The matrix does not need tobe fully populated. Switches can be removed if they are always open,replaced by shorts if they are always closed, or combined if they areswitched simultaneously (see e.g., FIG. 7).

The mixer module 406 includes a number of mixers (e.g., 406 a, 406 b,406 c, 406 d) having respective first and second inputs and havingrespective outputs. A first input of each mixer is coupled to a localoscillator (LO) line 410 on which an LO signal having an LO frequency isreceived. A second input for each mixer is coupled to an output of theswitch matrix 404. The outputs of the mixers are coupled to a sharedoutput 412. Upon receiving the LO signal and the signal from the switchmatrix, a mixer outputs a mixed signal the shared output 412, where themixed signal exhibits sums and differences of the frequencies of the twoinput signals. The number of mixers can be any number, and in someembodiments the number of mixers can be different from the number of DACcolumns.

As will be appreciated in more detail below, the control block 408 isconfigured to provide a control signal to the switch matrix 408 toselectively couple the output of the various current sources to thevarious mixers via the switches.

An example of how the circuit of FIG. 4 can operate is now discussedwith regards to FIG. 5. In FIG. 5's example, the current sourcesS_(0,0)-S_(k,2) are each configured to drive a unit current (e.g., 1 μAof current in this example). For example, in many embodiments thecurrent sources can be realized as MOS-type transistors, which all haveequal width to length ratios. The mixers in this example are alsoassumed to have the same geometries as one another. This configurationis advantageous in some respects because it may help to provide bettermatching and less noise than other embodiments where differentgeometries are used for the current sources and/or mixers. Of course,the present disclosure is not limited to current sources (or mixers)having the same size, and in other embodiments current sources (ormixers) could be sized differently from one another.

In 502 of the chart, a digital value of 001001 (of which the first threebits are provided to row decoder 402 and the second three bits areprovided to column decoder 404) enables the current sources on Row0 andColumn0 of the DAC 402 (i.e., current source S_(0,0) is enabled). Thecontrol signal to the switch matrix 404 is set to 0×001 (i.e.,000000000001), which couples the first column of the DAC to the firstmixer 406 a. In this way, 1 μA of current is delivered to mixer 406 a,which delivers a first output power to an RF antenna downstream of themixer module.

In 504 of the chart, a digital value of 001001 again enables the currentsource on Row0 and Column0 (i.e., current source S_(0,0) is enabled).However, the control signal is now set to 0×080 (i.e., 000000000100),which couples the first column of the DAC to the second mixer 406 b,such that 1 μA of current is now delivered to the second mixer 406 b. At506 and 508, the control value is changed to steer the 1 μA of currentto the third mixer 406 c and fourth mixer 406 d, respectively.

In 510, the digital value is changed to 001011, which enables thecurrent sources on Row1 and Columns1-2 (i.e., current sources S_(0,0) ;S_(0,1) are enabled). Depending on how the control bits are set, theswitch matrix 404 can deliver current from both sources to a singlemixer (as shown by 512 where a 2 μA current summed from S_(0,0) ;S_(0,1) is delivered to various individual mixers); or can deliver thecurrents to different mixers (as shown by 514, where 1 μA currents fromS_(0,0) ; S_(0,1) are delivered to different mixers).

Reference numerals 516-528 show other conditions in which the differentamounts of current are steered from the DAC 402 to the mixer module 406to facilitate desired functionality. It will be appreciated that FIG. 5is merely a non-limiting example, and that it in no way limits the scopeof the present disclosure.

FIG. 6 shows an example of a mixer 600 (e.g., one of mixers 406 a-406 din FIG. 4) in accordance with some embodiments. The mixer 600 includes afirst pair of transistors 602 a, 602 b having respective controlterminals on which a differential local oscillator (LO) signal isreceived. Respective sources of the first pair of transistors arecoupled to a DAC via a switch matrix. Respective drains of the firstpair of transistors are coupled to a second pair of transistors 604 a,604 b. The second pair of transistors receives an enable signal on theirrespective gates. Because of this configuration, the first and secondpairs of transistors 602, 604 can mix the signal from the DAC with theLO signal, and selectively deliver a modulated signal to a poweramplifier and RF antenna downstream of the mixer 600.

FIG. 7 shows another embodiment of a circuit 750 in accordance withanother embodiment. In this embodiment, the DAC output columns col.1though col. N−1 are shorted to one another, while DAC output column col0is selectively coupled to the other columns via a switching element 752.The control block 752 provides a control signal to the switching elementto selectively couple col0 to the other columns and to selectivelyenable the appropriate mixers. Hence, this embodiment provides a limitedswitching matrix that allows less flexibility than that of FIG. 4'sembodiment. Although it provides less flexibility, however, this limitedswitching matrix with a single transistor also requires less circuitrythan FIG. 4's embodiment, which correspondingly provides lower powerconsumption and a lower overall cost due to silicon area savingsrelative to the circuit of FIG. 4. It will be appreciated that anynumber of variations are contemplated as falling within the scope ofthis disclosure. For example, additional switching elements could bepositioned between the other columns to provide more flexibility, butalso correspondingly introducing more complexity and area requirementsfor the end circuit.

FIG. 8 shows a method 800 in accordance with some embodiments. Whilethis method is illustrated and described below as a series of acts orevents, the present disclosure is not limited by the illustratedordering of such acts or events. The same is true for other methodsdisclosed herein. For example, some acts may occur in different ordersand/or concurrently with other acts or events apart from thoseillustrated and/or described herein. In addition, not all illustratedacts are required and the waveform shapes are merely illustrative andother waveforms may vary significantly from those illustrated. Further,one or more of the acts depicted herein may be carried out in one ormore separate acts or phases.

The method starts at 802, when a first multi-bit digital value isconverted to a corresponding first output current. This can be carriedout by a DAC.

In 804, the first output current is steered along a first current pathbased on a control signal. In many implementations, the control signalcan be provided from a control block (e.g., as discussed with respect toFIG. 4). However, in other implementations, the control signal cancorrespond to the multi-bit digital value itself.

In 806, the current steered along the first current path is mixed with alocal oscillator signal to facilitate transmission of a radio-frequency(RF) signal at a first transmit power during a first time period. Thisblock can be carried out by a mixer module in many implementations.

At 808, the method converts a second multi-bit digital value to acorresponding second output current. The second multi-bit digital valuecan differ from the first multi-bit digital value.

At 810, the second output current is selectively steered along a secondcurrent path based on the control signal.

At 812, the current steered along the second current path is mixed withthe local oscillator signal to facilitate transmission of aradio-frequency (RF) signal at a second transmit power during the secondtime period. The second transmit power differs from the first transmitpower. Although not shown in FIG. 8, it will be appreciated that themethod 800 can continuously change its multi-bit digital value andcontrol signal to transmit an RF signal over a number of differenttransmission powers.

Although the disclosure has been shown and described with respect to oneor more implementations, equivalent alterations and modifications willoccur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Forexample, although the concept of an RF DAC has been described above withrespect to polar modulators, it will be appreciated that the concept isequally applicable to other modulations techniques, such as I/Qmodulation. Thus, in other embodiments, the RF DAC with current steeringis included in an IQ transmitter rather than a polar transmitter asillustrated herein. The disclosure includes all such modifications andalterations and is limited only by the scope of the following claims. Inparticular regard to the various functions performed by the abovedescribed components (e.g., elements and/or resources), the terms usedto describe such components are intended to correspond, unless otherwiseindicated, to any component which performs the specified function of thedescribed component (e.g., that is functionally equivalent), even thoughnot structurally equivalent to the disclosed structure which performsthe function in the herein illustrated exemplary implementations of thedisclosure. In addition, while a particular feature of the disclosuremay have been disclosed with respect to only one of severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and advantageousfor any given or particular application. In addition, the articles “a”and “an” as used in this application and the appended claims are to beconstrued to mean “one or more”.

Furthermore, to the extent that the terms “includes”, “having”, “has”,“with”, or variants thereof are used in either the detailed descriptionor the claims, such terms are intended to be inclusive in a mannersimilar to the term “comprising.”

What is claimed is:
 1. A circuit, comprising: a digital to analogconverter (DAC) configured to convert a time-varying, multi-bit digitalvalue to a corresponding time-varying output current; a mixer moduledownstream of the DAC and comprising a plurality of mixers; and acontrol block configured to selectively steer output current from theDAC to different mixers of the mixer module; wherein the DAC is directlyconnected to the mixer module.
 2. The circuit of claim 1, wherein theDAC comprises: a plurality of current sources that are independently andselectively enabled based on the time-varying multi-bit digital valueprovided to the DAC.
 3. The circuit of claim 2, wherein the plurality ofcurrent sources comprise a plurality of transistors, respectively, andwherein a first transistor of a first current source has the samedimensions as a second transistor of a second current source.
 4. Thecircuit of claim 2, further comprising: a plurality of switches arrangedto selectively couple the plurality of current sources to the pluralityof mixers based on a control signal from the control block toselectively steer output current from the DAC to different mixers of themixer module.
 5. The circuit of claim 1, wherein a power amplifier iscoupled downstream of the mixer module, and wherein the power amplifieris adapted to transmit RF signals at different powers over an RFantenna.
 6. The circuit of claim 5, wherein the different powers areassociated with at least two of the following communication standards:GMSK, EDGE, UMTS, LTE, WIMAX, 802.11, or Bluetooth.
 7. The circuit ofclaim 1, wherein a mixer of the plurality of mixers comprises: a firstpair of transistors having respective source/drain regions coupled tothe DAC; and a second pair of transistors having respective controlterminals on which an enable signal is received, wherein the second pairof transistors is operable to selectively couple an output of the firstpair of transistors to an RF antenna.
 8. The circuit of claim 7, furthercomprising: a power amplifier coupled to an output of the mixer, whereinthe power amplifier has an output configured to be coupled to the RFantenna.
 9. The circuit of claim 1, wherein the plurality of mixers areall of equal size.
 10. A circuit to facilitate transmission of a radiofrequency (RF) signal, comprising: a plurality of mixers each having apair of inputs and an output; a digital to analog converter (DAC)comprising: a plurality of current sources that are independently andselectively enabled based on a multi-bit digital value provided to theDAC; a switch matrix comprising a plurality of switching elementscoupled between the DAC and the plurality of mixers, wherein a firstswitch in the switch matrix has a first contact coupled to a first inputof a first mixer and a second contact coupled to an output of a firstcurrent source; and a control block to provide a control signal to acontrol terminal of the switch to selectively couple the first input ofthe first mixer to the output of the first current source via the firstswitch; wherein the DAC is directly connected to the plurality ofmixers.
 11. A method of operating a transmission path in a transmitter,comprising: generating a programmable time-varying current; selectivelysteering the programmable time-varying current to a plurality of mixers;and mixing an unfiltered portion of the programmable time-varyingcurrent with a local oscillator signal at each of the selected pluralityof mixers to form one or more RF signal portions.
 12. The method ofclaim 11, wherein generating the programmable time-varying currentcomprises: receiving a multi-bit digital work indicating a desiredoutput power of the transmitter; and selectively enabling one or morecurrent sources to generate one or more distinct currents thatcollectively comprise the programmable time-varying current.
 13. Themethod of claim 12, wherein the one or more current sources comprises anarray of M×N current sources, wherein M is an integer number of rows andN is an integer number of columns, and wherein the multi-bit digitalword dictates which of the M×N current sources contribute to form theprogrammable time-varying current.
 14. The method of claim 13, whereinthe number M rows dictates a number of the one or more distinctcurrents, and a number of activated current sources along a given columndictates a magnitude of a respective distinct current for the givencolumn.
 15. The method of claim 11, wherein selectively steering theprogrammable time-varying current to the plurality of mixers comprises:selectively activating a matrix of switches based on a control signal,wherein the matrix comprises an I×J array of switches, wherein I is aninteger number of row, and J is an integer number of columns, andwherein based on the control signal, J mixers, that are coupled to the Jcolumns of switches, are configured to selectively receive differingamounts of current via the switch matrix.
 16. The method of claim 11,wherein selectively steering the programmable time-varying current toone or more mixers comprises directly connecting a component generatingthe programmable time-varying current to the one or more mixers.
 17. Amethod of operating a transmission path in a transmitter, comprising:converting a first multi-bit digital value to a corresponding firstoutput current; selectively steering at least some of the first outputcurrent along a first current path based on a control signal; mixing thecurrent steered along the first current path with a local oscillatorsignal to generate a first radio-frequency signal at a first transmitpower during a first time period; converting a second multi-bit digitalvalue to a corresponding second output current; selectively steering atleast some of the second output current along a second current pathbased on the control signal; and mixing the current steered along thesecond current path with the local oscillator signal to generate asecond radio-frequency signal at a second transmit power during a secondtime period, wherein selectively steering at least some of the firstoutput current along a first current path comprises: receiving thecontrol signal; and selectively activating one or more switches in amatrix of switches based on the control signal, wherein a number ofcolumns in the matrix corresponds to a number of distinct currents asdictated by the control signal, and a number of rows in the matrixcorresponds to a maximum amount of current for a one of the distinctcurrents.
 18. The method of claim 17, wherein mixing the current steeredalong the first current path with a local oscillator signal comprises:receiving an enable signal from a control block; enabling a plurality ofmixers corresponding to a number of distinct current from the matrix ofswitches, wherein each of the plurality of mixers mix a respectivedistinct current to form a respective distinct RF signal portion; andsumming together all the distinct RF signal portions associated with anumber of enabled mixers to form the first radio frequency signal. 19.The method of claim 17, wherein converting the first multi-bit digitalvalue to a corresponding first output current is performed with adigital to analog converter (DAC), and wherein mixing the steeredcurrent along the first current path with a local oscillator signal isperformed with a plurality of mixers, and wherein selectively steeringat least some of the first output current along a first current pathcomprises directly connecting the first current path to the plurality ofmixers.